DE60035743T2 - Optical device for insertion / branching for ring networks using wavelength division multiplexing - Google Patents

Description

Technical area

These The invention relates generally to fiber optic communication networks, and especially adding and extracting signals in wavelength division multiplexed ring networks.

General state of the art

optical fiber be due to the advantages in terms of their speed and Bandwidth in the context of optical transmission more and more for preferred transmission medium for communication networks. Wavelength Division Multiplexing (WDM) Method, that many optical channels at different wavelengths for simultaneous transmission as a composite optical signal over a single optical fiber combined, is used to meet the increasing demand for greater speed and bandwidth for optical transmission applications to fulfill. With the youngest Advances in optical network technology pull system manufacturers now dense wavelength division multiplexed (DWDM) systems considering the For example, up to 80 or more optical channels (i.e., wavelengths) in have a single conductor. Revolutionized in this way the optical DWDM transport technology the telecommunications industry.

In Considering the numerous benefits associated with its use of WDM and DWDM in wide area networks is the WDM and DWDM technology now also considered for use on public transport networks, e.g. in regional metropolitan area networks, etc. Traditionally, mass transit networks have been implemented using Time Division Multiplexing (TDM) etc. implemented as Synchronous Optical Network (SONET) rings. Even though such SONET rings perform well the strong and steady increase in bandwidth and management needs Bandwidth the possibilities and the capacity from SONET-rings. There is therefore the desire, if possible low cost, huge capacity and protocol independence from WDM and DWDM to these local loop networks.

Especially for this, WDM and DWDM strengthened instead of the existing time-division multiplex systems on public transport networks There are many incentives to apply. For example, through the direct establishment of a packet or cell based transport on individual optical channels an efficient transport can be achieved. In addition, WDM and DWDM systems provide a larger bandwidth ready, and provide more flexibility in the management of dynamic Bandwidth requirements of today's users.

The However, implementation of WDM or DWDM in agglomeration networks brings Compared to long-distance networks special challenges yourself. For example, the Add / Drop requests much greater in agglomeration networks than in long-distance networks, there agglomeration networks typically on a geographically limited Room are more densely occupied with users. In addition, the traffic flow, the diversity traffic types and dynamic changes in traffic density in the context of adding and extracting traffic managing traffic in agglomeration networks complicated. The release these problems with the help of usual WDM and DWDM methods, as they are e.g. used in long haul applications, leads in the more costly agglomeration environment to significant increases of Cost and complexity.

Common approaches for optical add / drop multiplexing based e.g. typically insisting on an add / drop node the entire Signal power for a selected one wavelength to extract. Some examples of components used for the optical Add / Drop multiplexing are line-AWG (Arrayed Waveguide Grating) -Router, Fiber Bragg Grating (FBG), or Mach-Zehnder Filter (MZF), to name just a few. However, these devices have several Disadvantages, why their use for practical applications in Public transport networks, such as Ring nets is not desirable. Some of these Disadvantages are, for example: wavelength-dependent loss; Power loss and other transmission impairments due to bandwidth narrowing and group velocity dispersion; limited spectral bandwidth, poor scalability, and high Implementation costs.

in the Generally depends the cost-effectiveness of applying DWDM in urban site-connecting (inter-office - IOF) and access applications strongly from the cost of the state of the art optical Components, e.g. optical multiplexers / demultiplexers, optical amplifiers, optical Switches and WDM sources. Although the flexibility of bandwidth allocation a crucial plus point of this application, but the Cost of providing this capacity using pure DWDM techniques in this more cost-sensitive environment than too high.

What is needed is a more cost-competitive and technologically feasible solution for adding and subtracting optical signals to take advantage of WDM or DWDM in metropolitan area networks realize.

One Article called "Optically Amplified WDM Ring Network Incorporating Channel Dropping Filters "by Willner et al IEEE Photonics Technology Letters, IEEE INC., New York, USA, Volume 6, No. 6, June 1, 1994 (1994-06-01), Pages 760 to 763, XP000457241 ISSN: 1041-1135, discusses the use of channel extraction filters at each node of a WDM network.

Excerpts from one Textbook called "Architecture and Building Blocks of Lightwave Networks "Optical Fiber Telecommunications, XX, XX, 1997, pages 267-275, XP009047666, pages 267-275, discusses optical Ring networks based on optical amplifiers, dense WDM and SDH SONET.

One Article called "low-loss Add / Drop Multiplexes For WDM Lightwave Networks "by Giles et al., Proceedings IOOC International Conference on Integrated Optics and Optical Fiber Communication, 1995, Pages 66 to 67, XP000614126, discusses the use of optical Circulators and grids to form passive add / drop circuits.

U.S. Patent 5,786,916 discusses an optical wavelength exchange element and an optical wavelength exchange device.

Brief description of the invention

costs and optical losses associated with adding and Removing optical channels a wavelength division multiplexed (WDM) signal in a WDM ring network are opposite substantially reduced in the prior art in an add / drop arrangement, the optical broadband couplers in combination with wavelength conversion and suppression elements used. At each node in the WDM ring that uses an add / drop element, which is based on a broadband optical coupler, becomes a part the optical signal power of the entire WDM signal (i.e., all optical channels), such that one or more optical channels of particular wavelength at the node can be removed. Information (e.g., data) added to the node should be over fed an optical channel, the WDM signal over the same broadband coupler is added. Another part of the optical Signal power of the WDM signal (including added optical Channels) is passed through the node into the WDM ring.

According to one another aspect of the invention has at least one node in the WDM ring Wavelength conversion and suppression elements, to a disturbance between the optical channels reduce due to a recirculation of this optical channels can occur in the WDM ring (e.g., after an optical channel has passed its destination node). The conversion and the suppression of wavelengths is depending on the specific ring topology used, with the broadband coupler based Add / Drop arrangement is used, different. The add / drop arrangement according to the principles of the invention can be used in various WDM ring architectures including, without limitation, Path-switched rings and line-switched rings.

The Add / drop arrangement according to the principles The invention uses components that have low optical losses (e.g., low losses at the drop and pass paths) over one wide bandwidth (e.g., broadband), and rather based on passive rather than active methods, and so in comparison to earlier Arrangements reduce costs and complexity. Further will be Problems related to add / drop arrangements of the prior art avoided with the cascading of bandwidth reducing filters, by adding to it and removing optical channels be used in a WDM ring broadband coupler.

Brief description of the figures

One more comprehensive understanding The present invention will be apparent from a reading of the following detailed description of the invention with reference to the figures, wherein like elements are designated by like reference numerals, and wherein:

1 shows a typical ring network;

2A and 2 B are simplified block diagrams of typical add / drop arrangements for multiple wavelength optical systems;

3A and 3B are simplified block diagrams of broadband couplers that may be used in wavelength add / drop elements in accordance with the principles of the invention;

4 an embodiment of an add / drop arrangement showing the broadband coupler 3 used in a unidirectional Path Switched Ring (UPSR) network;

5 another embodiment of an add / drop arrangement according to the principles of the invention;

6A to 6D and 7A to 7D simplified network diagrams are the basic ideas of the invention in the context of communication in a UPSR network show;

8th a simplified block diagram of one of the nodes of the network 6A to 6D and 7A to 7D in accordance with the principles of the invention;

9A and 9B simplified network diagrams are showing the principles of the invention in the context of communication in a unidirectional Line Switched Ring (ULSR) network;

10 an embodiment of an add / drop arrangement showing the broadband coupler 3 in the ULSR network 9 used;

11 such as 12A and 12B simplified network diagrams illustrating the principles of the invention in the context of communication in a bidirectional 2-fiber Line Switched Ring (2F-BLSR) network;

13 an embodiment of an add / drop arrangement showing the broadband coupler 3 in the 2F BLSR network 11 and 12 used;

14A and 14B such as 15A and 15B simplified network diagrams are showing the principles of the invention in the context of communication in a 4-fiber switched line switched-ring (4F-BLSR) network; and

16 an embodiment of an add / drop arrangement showing the broadband coupler 3 in the 4F BLSR network 14 and 15 used.

Detailed description of the invention

To the better understanding The basic idea of the invention will initially be an overview of a typical ring network are given. In particular, a prototypical WDM ring will be described, having one or more network elements with optical add / drop capacity, e.g. optical add / drop multiplexers. For a general overview of ring networks including SONET / SDH rings and WDM rings see e.g. Kaminow et al., Optical Fiber Telecommunications, Volume IIIA, pages 269-275 and 567 to 573 (1997). It should be noted that although the basic ideas of the Invention in the context of single-ring configurations, the lessons also on multi-fiber overlays self-healing WDM rings, e.g. Multi-ring architectures applied can be. Although further the embodiments shown and described here in the context of a 4-node network, let the principles of the invention with a ring network apply to any number of nodes. In this sense are the embodiments shown and described herein as illustrative and in no way as limiting.

1 shows. a unidirectional patch-switched ring (UPSR) 100 with knots 101 to 104 (each referred to as nodes A to D), via optical fibers 110 and 111 are connected. The knots 101 to 104 may include network elements capable of receiving signals from the optical fibers 110 and 111 be transported to add and remove channels, as at the nodes 101 and 102 shown. The basics of operating an UPSR are well known to those skilled in the art. For example, UPSR networks in the SONET / SDH area are well known, see, for example, Bellcore Generic Requirements, GR-1400-CORE, "SONET Dual-Fed Unidirectional Path Switched Ring (UPSR) Equipment Generic Criteria", January 1999, M. Chow , "Understanding SONET / SDH Standards and Applications," pages 7-23 to 7-40 (1995), and W. Goralski, "SONET: A Guide to Synchronous Optical Networks," pages 342-366 (1997) a UPSR is self-healing through the use of a so-called working path and guard path, as well as through the use of head-end bridging and tail-end switching at the entrance and exit nodes.

In the example off 1 are the knots 101 to 104 via fiber optic cable 110 in a work path, and over fiber optics 120 connected in a protection path. Signals, for example, in the node 101 are accessed via a head end bridge to both optical fibers 110 and 111 directed, and spread across the working and protection path in opposite directions to the knot 102 out (as shown by the arrows). At knots 102 For example, a tail end switch may be used to provide signals from the work or protection path to exit at nodes 102 select. In this way, the ring is self-healing, as in the case of certain fault conditions in the UPSR 100 a communication between the nodes can be maintained.

In the case of a WDM-based UPSR, a multi-wavelength optical signal having many optical channels, each channel operating at a distinctive wavelength, is transmitted from each of the optical fibers 110 and 111 carried. To take advantage of optical transmission in a WDM-based UPSR, it is desirable to extract and add individual optical channels from the multi-wavelength signal at selected nodes in the ring. For example, it may be desirable to node 101 Add traffic over a specific optical channel and traffic to nodes 102 refer to. Accordingly, at each of the nodes 101 and 102 an optical add / drop capability is provided. For this purpose, typically optical add / drop multiplexers are used.

It It should be noted that additional Equipment, both optical and electronic, at each node may be necessary to redirect traffic in an appropriate manner, e.g. SONET add / drop multiplexers, cross mediators, ATM switches, IP router and similar. For the Purpose of understanding The basic idea of the invention is the exact nature of this other electronic and optical equipment for processing the added and taken traffic irrelevant.

Referring again to 1 For example, in a WDM-based UPSR, wavelength allocation can be a problem because the communication is unidirectional, and because signals are both bridge-coupled to the working and protection paths between the nodes. For example, the signals propagate in the optical waveguide 110 of knots 101 to knots 102 and of nodes 102 to knots 101 in the same direction. Likewise, the signals propagate between these nodes in the optical fiber 111 in the same direction. So if the same wavelength for a communication of nodes 101 at nodes 102 and of nodes 102 at nodes 101 is used, this wavelength is in both optical fibers 110 and 111 occupied over the entire ring, eg on the work or the protection path. Therefore, due to the one-to-one correspondence between each link and a single optical channel of a particular wavelength, ie, a dedicated wavelength, there is no possibility to reuse the wavelength. More specifically, a separate optical channel (eg at wavelength λ ₁ ) may be used for communication between the nodes 101 and 102 Another optical channel (eg at wavelength λ ₂ ) can be used for communication between the nodes 101 and 103 In this way, wavelength allocation in a WDM-based ring becomes an important factor, especially in the context of add / drop capacity in a WDM-based ring.

As previously described, the common approach for wavelength add / drop multiplexers is to extract all signal power for a selected wavelength at an add / drop node. Accordingly, existing add / drop arrangements typically include wavelength selective components for adding and subtracting individual optical channels from the composite multi-wavelength optical signal, that is, the WDM signal. However, these add / drop arrangements may have disadvantages, as will be described below. 2A and 2 B Figure 2 shows two examples of wavelength add / drop elements that provide flexible add / drop capacity for WDM applications.

The add / drop arrangement 2A has an optical demultiplexer 201 for demultiplexing the composite WDM signal into the optical channels of which it is constructed. Each optical channel in this example is connected to a series of optical switches 202 and a wavelength add / drop element 205 coupled. The wavelength add / drop element 205 For example, a Mach-Zehnder filter can be used to extract a single optical channel and add a single optical channel each associated with the same wavelength. The optical switches 202 are shown as 1 × 2 switches serving at a first position for normal passage of the optical channel, and at a second position for removing and / or adding traffic from the optical channel. An optical multiplexer 206 is then used to recombine the optical channels forming the signal into the composite WDM signal. Typically, they are optical amplifiers 210 provided to compensate for losses that occur in the add / drop arrangement.

Among other problems, these types of add / drop devices have high insertion loss and high cost, especially for systems with a high number of channels, due to the number of components required for a WDM application. Typical losses associated with the multiplexer 206 For example, they can be up to 20 to 24 dB. Another important disadvantage is the bandwidth narrowing effect that results from cascading the filters. It should also be noted that, although not shown, each requires a separate transmitter and receiver for each channel to be added or removed. Removing the optical switches 202 While reducing costs and losses, it introduces other problems with updates during operation, and so on. In particular, the use of 1 × 2 switches allows a relatively uninterrupted update of a system, such as including switches at system startup, while wavelength add / drop devices vary according to user requirements, and so forth.

2 B shows another example of an optical add / drop arrangement using fiber Bragg gratings as wavelength-selective elements. This arrangement is well known, see for example Giles et al., "Low Loss Add / Drop Multiplexers for WDM Lightwave Networks", Tenth International Conference on Integrated Optics and Optical Fiber Communication, Volume 3, Hong Kong, June 1995, pages 66 to 67. In this configuration, optical circulators are used 215 along with bars 216 used optical channels each via an optical demultiplexer 217 and a multiplexer 218 to remove or add. In operation are the grids 216 transparent to those optical channels to be transmitted and reflective to those optical signals to be extracted or added. As with the arrangement of the prior art, the cost and, to a lesser extent, the loss becomes problematic due to the number and complexity of the components. Also, bandwidth narrowing is still a problem as the signals propagate across successive grids, with updates to the service likely to interrupt the existing service.

In accordance with the principles of the invention, an advance over the prior art is achieved by adding and extracting optical channels using add-drop elements based on a broadband coupler to a WDM signal coupled with appropriate wavelength allocation and signal redirection the ring network. 3A and 3B show two exemplary broadband coupler arrangements that may be used in accordance with the principles of the invention, wherein 3A is useful for a single wavelength add / drop scenario, and 3B extends this concept to a multi-wavelength add / drop scenario by using appropriate multiplexed / demultiplexed components.

More specifically, shows 3A a simplified block diagram of the basic block of the add / drop arrangement according to the principles of the invention. A broadband coupler or a branch 300 (hereinafter referred to as coupler 300 in short, allow the extraction and / or addition of optical signals from or to a transmission device, eg an optical waveguide or the like. The coupler 300 has an entrance 301 for receiving a multi-wavelength optical WDM signal and an input 302 for receiving an optical channel of a particular wavelength to be added to the WDM optical signal. Because the coupler 300 a broadband coupler carries each output 304 and 305 a composite WDM optical signal, ie all wavelengths. However, the optical channel to be extracted from the composite WDM optical signal is extracted from the WDM optical signal passing through the output 304 while the WDM optical signal including the added optical channel is supplied through the output 305 provided.

Broadband couplers and branches and their operation are well known to those skilled in the art. Therefore, those skilled in the art will recognize that various broadband optical modulators may be used to practice the teachings of the present invention. It is generally envisaged that the coupler 300 may be any suitable optical device that distributes, splits, or otherwise couples optical power between two or more ports. In the context of the present invention, the coupler 300 therefore referred to as a broadband coupler, since it is provided that the coupler 300 having the necessary spectral bandwidth to: 1) receive a WDM signal having a plurality of optical channels of different wavelengths; 2) to divert a portion of the optical signal power of the WDM signal such that certain optical channels at a node can be extracted from the WDM signal; and 3) to provide another part of the optical signal power of the WDM signal for output to optical transmission devices.

In the embodiments shown and described herein, for carrying out the principles of the invention, a "20/80" broadband coupler is provided, such as the double window broadband coupler manufactured by E-Tek Dynamics Inc. In this exemplary coupler, approximately 20% of the optical signal power of the optical signals passing through the inputs 301 and 302 are fed, branched off and via the branch outlet 304 while providing about 80% of the optical signal power over output 305 provided for the WDM output signal. It is to be understood that this example is illustrative only, as other coupling and branch breaking values may be used in carrying out the teachings of the invention. For example, it is well known that the coupling ratio of coupler 300 can be varied according to the design and performance parameters to obtain a desired amount of light, which is the branch output 304 and the exit 305 is supplied. In particular, the amount or fraction of optical signal power diverted from an optical fiber depends on the particular design, and may be based on parameters such as optical transmitter power, receiver sensitivity, or conductor loss, to name just a few examples. By way of illustration in the embodiments shown and described herein, the desired range of dropped power may be between 0.5 dB and 3 dB, eg at 1 dB. Again, these values are illustrative only and depend on many factors well known to those skilled in the art.

3B shows how the coupler 300 can be used with other components, such as an optical multiplexer 310 and an optical demultiplexer 311 to add and extract a plurality of optical channels of different wavelengths to the WDM optical signal. In every other respect are the operation and features of the coupler 300 similar to already for 3A and should not be repeated here for reasons of scarcity.

Again referring to the USPR 100 out 1 is provided that one or more nodes 101 to 104 have an add / drop arrangement, the coupler 300 ( 3A and 3B ) used in accordance with the principles of the invention. In particular shows 4 an embodiment of an add / drop arrangement according to the principles of the invention, the coupler 300A and 300B for use in the UPSR 100 used. As shown, the add / drop arrangement has the coupler 300A on the fiber optic cable 110 ie the work path of UPSR 100 out 1 is coupled. Likewise, the coupler 300B to the optical fiber 111 ie the protection path of UPSR 100 coupled. Both couplers 300A and 300B received at the entrances 301A respectively. 301B the WDM signal having a plurality of optical channels of different wavelengths, shown here as λ ₁ , λ ₂ , ... λ _n . As previously described, head end jumper coupling is typically performed on both the working and protection paths of a UPSR for the same signal.

The couplers 300A and 300B are also at entrances 302A and 302B each to optical transmitter 315A respectively. 315B each optical transmitter provides an optical channel of a particular wavelength, here shown as λ _n-1 , to be added to the WDM signal. It is envisaged that the optical transmitter 315A and 315B are fixed or adjustable type, wavelength selective, direct or external modulated, etc. Specific examples of various devices used to provide an optical carrier (ie, an optical channel of a particular wavelength) and to modulate data onto the optical carrier are well-known to those skilled in the art known. Therefore, components for adding traffic (eg, data) to the WDM signal are collectively referred to as optical transmitters for ease of explanation and illustration. According to another aspect of the invention, which will be described in more detail below in the context of specific network configuration examples, the optical transmitters 315A and 315B either separate devices, as in 4 shown, or implemented as a single optical transmitter. In the latter case, an optical transmitter may be coupled to a divider (not shown), eg a 1 × 2 power divider, to each of the couplers 300A and 300B to provide an optical channel (ie with the same wavelength). Other modifications will also be apparent to those skilled in the art.

The couplers 300A and 300B are also at exits 304A and 304B each to optical filters 316A respectively. 316B coupled. As previously described, the couplers are 300A and 300B Broadband coupler, which is why only a part of the optical signal power of the composite optical WDM signal (ie, λ ₁ , λ ₂ , ... λ _n ) is branched off at the couplers. Therefore, the optical filters 316A and 316B is required to filter out the optical channel of a particular wavelength to be extracted from the WDM optical signal, here referred to as λ _drop , where λ _{drop is} for one or more constituent channels (ie, λ ₁ , λ ₂ , ... λ _n ) stands. Optical filters as well as other components for separating or splitting the composite optical WDM signal into the signal building optical channels are well known to those skilled in the art.

The respective filtered optical channel from the working and protection paths, ie the optical setup channel to be extracted from the WDM optical signal, is then applied to an optical protection switching element 318 provided. For example, the switching element 318 in the UPSR 100 the tailend switching function provides for selecting the signal provided from either the working or protection path, depending on the particular protection circuitry used. The selected optical channel is then adapted for appropriate processing at the drop node to a suitable optical receiver 320 fed. Specific examples of various devices used to receive and process a modulated optical carrier (ie, an optical channel of a particular wavelength) are well known to those skilled in the art. For ease of explanation and illustration, the components for extracting traffic (eg, data) from the WDM signal are therefore collectively referred to as optical receivers.

Because the couplers 300A and 300B Further, part of the optical signal power of the WDM composite optical signal (ie, λ ₁ , λ ₂ , ... λ _n ) including the added optical channel (eg, λ _n-1 ) is propagated respectively at the working and protection paths, respectively the exits 305A and 305B on the optical fiber 110 respectively. 111 provided. In this way, the broadband couplers support 300A and 300B also a process of taking and continuing.

It should be noted that modifications of the above embodiment may also be made to allow for adaptation to electronic protection switching. example way, instead of the optical filter 316A and 316E optoelectronic receivers are used, followed by an electronic switch, eg a 2x1 switch, to switch the tail end switch function 318 perform.

The use of broadband couplers to add and remove signals could trigger a potential problem with crosstalk effects. More specifically, there is a potential for the signal to leak into the extracted signal because signals are both introduced (ie, added) and extracted (ie, extracted) by the same branch or coupler. This undesirable effect can be exacerbated by the fact that the introduced signal typically has a higher optical signal power than the extracted or branched signal. For example, this leakage potential could be the result of the channel isolation and crosstalk characteristics of the respective optical filters, demultiplexers, etc., used to filter out the optical channel of a particular wavelength to be extracted from the WDM signal. According to shows 5 an embodiment according to the principles of the invention to reduce or eliminate this undesirable effect by means of an adaptive balance or an adaptive cancellation.

In particular shows 5 a coupler 300 having similar characteristics as already described in the preceding embodiments. For purposes of brevity, only the differences between this embodiment and the previously disclosed embodiments will be described here. As shown, the coupler is 300 over exit 304 to an optical demultiplexer 325 coupled. The demultiplexer 325 receives the part of the composite WDM signal coming from the coupler 300 is dropped, and separates the composite WDM signal into the individual optical channels of different wavelengths. Due to the aforementioned limitations of devices such as optical demultiplexers in crosstalk and channel isolation, it is possible that the dropped WDM optical signal contains unwanted signal components from the optical channel at the input of the coupler 300 is added, shown here as λ _{n + 1} . Therefore, even the single optical channel to be extracted at the node, shown here as λ _drop , can contain these unwanted signal components.

To remedy this problem, the single optical channel to be extracted at a node (λ _drop ) is for conversion into an electrical signal to a device such as a photodetector 326 coupled. The operation of photodetectors and equivalent devices is well known to those skilled in the art. The electrical signal can then continue in the usual way to an amplifier 327 be coupled. The amplified electrical signal is then a subtraction circuit 328 supplied to the signal that at the node (ie at the input 302 of the coupler 300 ) from which signal can be subtracted, taken at the node. Other methods for removing the unwanted signal components from the dropped signal will be readily apparent to those skilled in the art, and are therefore provided in the present teachings.

Around a better understanding to obtain the basic idea of the invention, should now several exemplary ring network configurations will be described which the use add-drop arrangements based on broadband couplers, which in the above embodiments have been described.

Example 1 (Unidirectional Path Switched Ring)

6A to 6D show an exemplary unidirectional path-switched ring (UPSR) 400 in which the principles of the invention can be applied. As shown, UPSR 400 node 401 to 403 as well as a special function node 405 in the following for reasons to be discussed as a termination node 405 should be designated. The knots 401 to 403 and the termination node 405 are via fiber optic cables 410 and 411 , which below each as a work path 410 or as a protection path 411 be referred to, connected in a ring configuration. The basics of operating an UPSR are well known and have been outlined in the description 1 briefly outlined. The knots 401 to 403 may each have the add-drop arrangement based on broadband couplers, which in the above embodiments (eg 3 and 4 ) has been described. However, the example scenarios show 6A to 6D a specific example of communication between the nodes 402 and 403 (ie nodes B and C). Therefore, it is assumed that at least the nodes 402 and 403 in each case the broadband coupler based add / drop arrangement 4 exhibit.

In addition, in this embodiment, the termination node is due to optical self-interference problems that may arise with closed ring architectures 405 required. As is well known, these problems can occur when an optical channel of a particular wavelength used to carry traffic between two nodes circulates endlessly in the ring. In general, in a ring no circulation (ie recirculation) is allowed to the self to avoid interference problems. In accordance with the principles of the invention, self-interference effects at the termination node can be substantially reduced by converting incoming optical signals into electrical signals, and then back to optical signals. More specifically, the termination node becomes 405 used in the ring to serve as the starting and terminating point of the ring, some signals can be added at the node, some signals can be taken at the node, some signals can be expressed by the node (eg normal transmission), and Some signals at the node can be terminated or otherwise suppressed. For purposes of illustration only, the function of the termination node may be performed at a central node (eg, the headquarters location), or at a common cross-connect node that interfaces with multiple rings. It should also be noted that the termination node 405 can also be used to monitor the network and to send administrative information to the other nodes in the ring.

8th FIG. 5 is a simplified block diagram of one embodiment of the termination node in accordance with the principles of the invention. FIG. In short, the termination node includes components for demultiplexing and multiplexing WDM optical signals, components for converting wavelengths of individual optical channels, and components for adding and dropping signals. The termination node 405 out 8th can in the UPSR 400 out 6 be used, with the termination node to the working path 410 and the protection path 411 coupled to the ring. At the termination node 405 is the optical demultiplexer 420 to the work path 410 coupled to separate the optical WDM signal into individual optical channels. Some of the optical channels are to wavelength converters 421 coupled. Wavelength converters, such as optical translation modules (OTUs), are well known to those skilled in the art. Using the example of an OTU, an optical signal is converted into an electrical signal and then back to an optical signal of a different wavelength. The need for wavelength converters is said below in connection with the operation of the UPSR 6 be described in more detail. Some of the demultiplexed optical channels become at the termination element 450 terminated or otherwise suppressed. Many different methods and devices for terminating optical signals, such as photodetectors and receivers, etc., are readily apparent to those skilled in the art.

After suitable wavelength conversion or termination, the individual optical channels are then received by the optical multiplexer 422 multiplexed into a composite optical WDM signal. Although a complete demultiplexing of all channels and a subsequent multiplexing at termination nodes 405 is provided, there are several methods and wavelength plans that can be implemented to achieve this function. An example is a WAR (Arrayed Waveguide Router) multiplexer / demultiplexer, such as the so-called Dragone router, see U.S. Patent 5,002,350 , which is cited here by cross reference. Other solutions, however, will be apparent to those skilled in the art and are therefore provided by the present teachings.

To the protection path 411 are an optical demultiplexer 420 , a multiplexer 422 , Wavelength converter 421 and a termination element 450 coupled, all of which perform the same function as before for the corresponding components on the working path 410 described. As shown, is a wavelength add / drop element 490 each to the work and the protection path 410 and 411 coupled to add or remove optical channels as needed. For ease of illustration, the wavelength add / drop element is 490 as a single functional block, but it will be understood that the wavelength add / drop element 490 using the broadband coupler based add / drop arrangement 4 can be implemented.

In operation, in the UPSR 400 Signals are added and removed as in 6 shown. Although a composite WDM signal having optical channels of different wavelengths surrounds the UPSR 400 For ease of illustration, only those optical channels actually added and removed at the selected node are indicated by dotted arrows in the ring for ease of illustration. 6A and 6B show a communication from node B ( 402 ) to node C ( 403 ). Node B sends clockwise to work path 410 ( 6A ) and counterclockwise on the protection path 411 ( 6B ) Data on the optical channel λ ₁ . In 6A branches node C, which uses a broadband coupler based add / drop arrangement as shown in FIG 4 is shown, a portion of the optical signal power of the optical WDM signal from the working path 410 such that traffic carried by the optical channel λ ₁ can be extracted at node C. The remaining optical signal power in the optical channel λ _{1 of} the WDM signal at working path 410 is then to termination node 405 from the scheduling element 450 terminated. One reason for terminating or otherwise suppressing the optical channel λ ₁ after it has passed its destination node (node C) is to prevent any interference that would otherwise occur if the optical channel could continue to circulate to node B where it is towards the ring was added.

As in 6B As shown, the WDM signal (including the optical channel λ ₁ ) moves counterclockwise on the protection path 411 , If it is from the termination node 405 is received, the wavelength of the optical channel λ _{1 is converted} to the optical channel λ ₃ . One reason for converting the wavelength of an optical channel that has not yet passed its destination node is also to avoid interference that would otherwise occur if the optical channel of the original wavelength, eg, the optical channel λ ₁ , back to node B circulate where he was originally added to the ring. As shown, node C branches a portion of the optical signal power of the WDM optical signal from the protection path 411 for traffic carried by the optical channel λ ₃ to be extracted at node C. The remaining optical signal power in the optical channel λ _{3 of} the WDM signal on protection path 411 is then at the termination node 405 from the scheduling element 450 terminated.

The wavelength assignments in the UPSR 400 and the use of the termination node 405 in 6A and 6B illustrate an important aspect in terms of reuse of wavelengths. In particular, because a broadband coupler branches off a portion of the optical signal power of the WDM optical signal (ie, all wavelengths), as opposed to extracting certain wavelengths of the WDM optical signal at a particular node, the WDM optical signal (ie, all Wavelengths) further through the ring. In this way, individual wavelengths for the optical channels added and removed between the nodes on the ring can not be reused. For example, a wavelength used for the optical channel may be the traffic of nodes 402 to knots 403 (added to B and taken from C) can not also be used for the optical channel, the traffic of nodes 403 to 402 (added to C and taken from B). Accordingly, an add / drop arrangement according to the principles of the invention requires different wavelengths to support each of the links in the ring, ie, λ ₁ for B to C, λ ₂ for C to B, and so on.

Likewise show 6C and 6D Communication from node C to node B. Node C transmits data on the optical channel λ ₂ clockwise on the working path 410 ( 6C ) and counterclockwise on the protection path 411 ( 6D ). As in 6C shown, the termination node converts 405 the wavelength of the optical channel λ ₂ on the optical channel λ ₃ for the reasons described above. As shown, node B branches a portion of the optical signal power of the WDM optical signal from the working path 410 for traffic carried on the optical channel λ ₃ to be extracted at node B. The remaining optical signal power on the optical channel λ _{3 of} the optical WDM signal to working path 410 will then be on the work path 410 through the termination element 450 at termination nodes 405 terminated. As in 6D Node B branches a portion of the optical signal power of the WDM optical signal from the protection path 411 so that traffic carried on the optical channel λ ₂ can be taken out at node B. The remaining optical signal power in the optical channel λ _{2 of} the WDM optical signal on the protection path 411 is then at the termination node 405 through the termination element 450 terminated.

In the preceding embodiment 6 For example, a respective node adds an optical channel of the same wavelength at both the working and protection paths, but receives and removes channels of different wavelengths from the working and protection paths. In another alternative embodiment, it may be desirable for a node to add different wavelength optical channels to the working and protection paths, but to receive and extract optical channels of the same wavelength. This latter example is in 7A to 7D shown. As to the embodiment of 7A to 7D in terms of operation, the same basic principles apply as for 6A to 6D described, they should not be described again for reasons of scarcity. Other modifications which are within the spirit and scope of the present invention will be apparent to those skilled in the art and are provided by the present teachings.

Example 2 (Unidirectional Line Switched Ring)

The Add / drop arrangement according to the principles The invention may also be advantageous to a second type of ring network the so-called unidirectional Line Switched Ring (ULSR) network. Again, the basic operating principles of a ULSR network are good known. In short, nodes in a ULSR communicate through the Conducting signals in the same direction, i. unidirectional, and although only on the work path. For the case of a node failure, a cable cut-off or a Error states implement nodes in the vicinity of the point of failure a so-called "loopback", where signals over the Protection path are redirected in the direction that leads to the one in the work path is opposite.

In accordance with the principles of the invention, in a ULSR, WDM signals can be generated using a broadband coupler-based add / drop-on order to be added and removed. 9A and 9B specifically show an exemplary unidirectional line switched ring (ULSR) 500 in which the principles of the invention can be applied. As shown, ULSR 500 node 501 to 503 and a termination node 505 on. The knots 501 to 503 and the termination node 505 are via fiber optic cables 510 and 511 , hereinafter each as a work path 510 or protection path 511 designated connected in a ring configuration. As in the previous UPSR example, the nodes 501 to 503 each have a broadband coupler based add / drop arrangement. However, the example scenarios show 9A to 9B a specific example of communication between the nodes 502 and 503 (ie nodes B and C) in the event of an error between the nodes 501 and 502 (ie nodes A and B). It is assumed that at least the nodes 502 and 503 each have a broadband coupler based add / drop arrangement.

Again, for ease of illustration only those optical channels are shown by the dotted arrows in the ring which are actually added and extracted at the selected node, although the composite WDM signal having optical channels of different wavelengths moves through the ring. In 9A sends node B over the optical channel λ ₁ on the working path 510 clockwise data to node C. Node C branches from the working path using a broadband coupler based add / drop arrangement in accordance with the principles of the invention (not shown) 510 a portion of the optical signal power of the optical WDM signal so that traffic carried by the optical channel λ ₁ , can be removed at node C. The remaining optical signal power in the optical channel λ _{1 of} the optical WDM signal on the working path 510 is then at the termination node 505 from the scheduling element 550 terminated.

As in 9B shown, sends node C via the optical channel λ ₃ on the working path 510 clockwise data to node B. For reasons similar to those already described in the previous embodiments, the termination node converts 505 the wavelength of the optical channel λ ₃ on an optical channel λ ₂ . Due to an error condition 560 between nodes A and B, both nodes A and B implement loopback switching according to well-known methods for line-switched rings. In this way, the optical WDM signal at node A becomes the working path 510 received and returned in a loopback on protection path 511 where it moves on to its destination, eg a node. At its destination node B, the optical WDM signal is returned to the working path in a loop back arbitration 510 directed. Node B, which uses a broadband coupler based add / drop arrangement in accordance with the principles of the invention (not shown), branches a portion of the optical signal power of the WDM optical signal from the working path 510 so that traffic carried by the optical channel λ ₂ can be extracted at node B. The remaining optical signal power in the optical channel λ _{2 of} the WDM optical signal moves on the working path 510 to the termination node 505 where it is from the termination element 550 is terminated.

It should be noted that in many scenarios, network traffic may not be self-healing if the termination node fails. For example, if the termination node fails and thereby causes neighboring nodes to implement loopback switching such that signals are not passed through the termination node 505 spread, it does not come to the appropriate conversion and suppression / termination of the wavelength. In this way, the mentioned interference problems could occur.

10 shows an embodiment of a broadband coupler-based add / drop arrangement used for adding and extracting signals in ULSR 500 ( 9 ) could be used. Professionals will understand that the arrangement in 10 a variant of in 4 shown and described embodiment for the UPSR example. Therefore, common elements and functions are not repeated here for the sake of brevity. Instead, only the relevant differences are explained, most of which involve coupling the add / drop arrangement to the working and protection paths 510 . 511 as well as the switching and routing of signals from these paths through the broadband coupler 601 ,

As shown, the add / drop arrangement has 600 a broadband coupler 601 , an optical transmitter 602 , an optical filter 603 , and an optical receiver 604 , which all work in a similar way as for the arrangement 4 described. However, the add / drop arrangement indicates 600 further at least two optical switches 610 and 611 which are shown here as 2 × 2 optical switches. The optical switches 610 and 611 can be measured using well-known devices such as an opto-electrical switch, mechanical optical switch, lithium niobate switch, polymer-based switch, and the like. be implemented. Those skilled in the art will readily appreciate other suitable optical signal redirecting apparatus in accordance with the principles of the invention.

In normal operation, eg without fault conditions, the switches are located 610 and 611 in a crossbar state. More specifically, signals are over the working path 510 in the switch 611 get to the coupler 601 mediated or otherwise directed. At the coupler 601 the addition and removal of optical channels takes place in the same way as for the in 4 shown embodiment described. The optical WDM signal, which is the coupler 601 leaves, moves on to switch 610 where it mediates or otherwise goes beyond the work path 510 is directed.

If an error occurs in the ring (eg error 560 in the ULSR 500 out 9 ), a node located adjacent to the fault (eg, node A or B) implements loopback switching and redirects signals accordingly. In one example, the switch 611 (Switch B) go into the so-called rail condition, and the switch 610 (Switch A) can remain in the crossbar state. In this scenario, signals are over the work path 510 in the switch 611 (Switch B) get through switch 611 directly in a loop on the protection path 511 back conveyed. Signals coming from the switch 610 (Switch A) over the protection path 511 will be received at path 615 mediates because the switch 610 (Switch A) is in a crossbar state. Because the switch 611 (Switch B) is in a track state, then signals from the protection path 511 through the coupler 601 where appropriate add / drop operations may take place, as previously described. Signals that the coupler 601 leave, then get off the switch 610 (Switch A), which is still in the crossbar state, to the working path 510 diverted. It should be noted that a change in states, eg, crossbar state or rail state, for each of the optical switches in the add / drop arrangement is dependent on the position of the error relative to the node.

Example 3 (Bidirectional 2-fiber line-switched ring)

The Add / drop arrangement according to the principles The invention may also be advantageous to another type of ring network the so-called Bidirectional Line Switched Ring (BLSR) network. As with UPSR and ULSR networks For example, BLSR networks are well known in the SONET / SDH domain, see e.g. Bellcore Generic Requirements, GR-1230-CORE, "SONET Bi-directional Line-Switched Ring Equipment Generic Criteria ", December 1996, M. Chow, "Understanding SONET / SDH Standards and Applications ", Pages 7-23 to 7-40 (1995), and W. Goralski, "SONET: A Guide to Synchronous Optical Networks ", Pages 342 to 366 (1997).

In accordance with the principles of the invention, in a BLSR, WDM signals may be added and dropped using a broadband coupler based add / drop arrangement at one or more nodes in the BLSR. In particular shows 11 an exemplary bidirectional 2-fiber line-switched ring (2F-BLSR) 650 to which the principles of the invention can be applied. The 2F-BLSR 650 has the same basic physical configuration as the previous ring networks. In particular, nodes are 651 to 653 and a termination node 655 via fiber optic cable 660 and 661 connected in a ring configuration. However, the difference between a 2F BLSR network and unidirectional rings is in the flow of traffic. In a 2F BLSR network, for example, is the bandwidth of each optical fiber 660 and 661 divided, such that one half is intended for work and one half for protection. Furthermore, the traffic flows in the optical fiber 660 clockwise, and in the optical fiber 661 counterclockwise.

Again, for ease of illustration, only those optical channels are represented by dotted arrows in the ring that are actually added and removed at selected nodes, although the composite WDM signal moves through the ring. In 11 (Normal operation) sends the node 652 (Node B) via the optical channel λ ₁ Clockwise data at node 653 (Node C), where the working bandwidth of the optical fiber 660 is used. Similarly, the node sends 653 (Node C) via the optical channel λ ₂ counterclockwise data at nodes 652 (Node B), where the working bandwidth of the optical fiber 661 is used. As in the previous embodiments, both nodes have 652 and 653 broadband coupler-based add / drop arrangements (not shown) to assist in the addition and removal of the optical channels λ ₁ and λ ₂ . Optical signals λ ₁ and λ ₂ become termination nodes 655 terminated in a similar manner and for reasons similar to those mentioned above.

12A and 12B show the operation of the 2F-BLSR 650 in the case of a mistake 670 between nodes B and C, where 12A shows communication from node B to node C, and 12B shows a communication from node C to node B. In general, loopback switching is used, as described previously for the ULSR example, with the only difference in traffic flow between the working and guard bandwidths in the optical fibers 660 and 661 consists. In particular, nodes B and C implement in response to errors 670 a loopback exchange.

In 12A Node B, which is in the loopback mode, routes the WDM optical signal (including the optical channel λ ₁ ) from the working bandwidth of the optical fiber 660 on the guard band width of the optical waveguide 661 around. The optical channel λ ₁ is not connected to termination nodes 655 terminated because he has not yet reached his destination. The node C performs loopback switching of the WDM optical signal from the guard bandwidth of the optical fiber 661 back to the working bandwidth of the optical fiber 660 by. Using the broadband coupler based add / drop arrangement according to the principles of the invention (not shown), traffic carried by the optical channel λ ₁ is then extracted at node C. The remaining optical signal power in the optical channel λ _{1 of} the optical WDM signal on the working bandwidth of the optical waveguide 660 is then connected to termination nodes in a similar manner as previously described 655 terminated. In 12B becomes the optical channel λ ₂ from node C to node B in a similar manner as previously described by the 2F-BLSR 650 diverted. The main difference is that for the WDM optical signal (including the optical channel λ ₂ ) at node C, loopback switching is from the working bandwidth of the optical fiber 661 (counterclockwise) to the guard band width of the fiber optic cable 660 (clockwise), and vice versa at node B.

Another significant difference in the 2F-BLSR 650 is that of the termination node 655 still must be able to optical channels of specific wavelengths in the two optical fibers 660 (clockwise) and 661 (counterclockwise) to pass or terminate. However, wavelength conversion is not mandatory, which may result in fewer wavelengths being used to allow for the addition and extraction of signals between nodes in the ring. For example, wavelength conversion is not necessary if all connections between any two nodes are not through the termination node in the absence of errors 655 be directed. In this case, the termination node terminates 655 all wavelengths of both optical fibers 660 and 661 or suppress it in another way. If there is an error in the ring and loopback arbitration is initiated to isolate the error, the termination node will only pass those wavelengths that have not yet passed its destination node.

13 shows an illustrative embodiment of a broadband coupler based add / drop arrangement 700 that at the knot 651 to 653 in the 2F-BLSR 650 out 11 and 12 can be used. The structure and operation of the add / drop arrangement 700 in 13 are similar to before for 10 described, with the difference that another broadband coupler and corresponding components are used for adding and removing individual optical channels. In particular, the add / drop arrangement 700 a pair of broadband couplers 701A and 701B on, a pair of optical transmitters 702A and 702B , a pair of optical filters 703A and 703B , a pair of optical receivers 704A and 704B , and a pair of optical switches 710 and 711 to the optical fibers 660 and 661 to pair. The additional coupler 701B and the associated stations 702B , Filters 703B and receiver 704B are used, for example, because signals from the working bandwidth of both optical fibers 660 and 661 can be added and removed. As with the previous embodiments, the switches operate 710 and 711 in a crossbar state, when the ring is in normal operation (eg without error). Likewise, the optical switches change 710 and 711 their state to perform the loopback functions, eg, rail state and crossbar state, depending on the position of the error relative to the node.

Example 4 (Bidirectional 4-fiber line-switched ring)

A Another well-known optical ring network architecture is the so-called bidirectional 4-fiber line-switched ring (4F-BLSR) whose construction and operation professionals are well known. The 4F-BLSR is short taken a similar one Operation on like the 2F-BLSR, with the difference being that for everyone the following traffic flows a separate optical fiber is provided: clockwise work; Work traffic counterclockwise; Protective traffic in a clockwise direction; and protective traffic counterclockwise.

14A and 14B show traffic flow in an exemplary bi-directional 4-fiber Line-Switched Ring (4F-BLSR) 800 under normal conditions while 15A and 15B show the flow of traffic in case of a fault in the ring. As shown, nodes are 801 to 804 via fiber optic cable 810 (Working path in clockwise direction), optical fiber 811 (Working path counterclockwise), optical fiber 820 (Protection path in clockwise direction) and optical fiber 821 (Anti-clockwise protection path) connected in a ring configuration. For reasons which will be described in more detail below, the clockwise and counterclockwise working paths, namely the optical fibers, form 810 respectively. 811 , no closed ring. By contrast, the protective paths running in a clockwise and counterclockwise direction, namely the optical waveguides 820 respectively. 821 , a closed ring.

In 14A sends the node 802 (Node B) using the clockwise working conductor 810 Data over the optical channel λ ₁ clockwise at nodes 803 (Node C). In 14B the node C sends in the counter-clockwise working conductor 811 via optical channel λ ₁ in the counterclockwise direction data to node B. are For ease of illustration, only those optical channels that are actually added to the selected node and removed, as shown by dotted arrows in the ring even though the composite WDM signal through the Ring moves. In the 4F-BLSR 800 For example, WDM signals may be added and extracted using a broadband coupler-based add / drop arrangement (not shown) as described in the previous embodiments (eg, optical channels λ ₁ between nodes B and C).

A significant difference from the other embodiments related to operation concerns the termination and conversion of wavelengths. Especially since the clockwise working ladder 810 and the counter-clockwork work manager 811 do not form closed rings, requires 4F-BLSR 800 no special termination node. Instead, interference is avoided simply by not connecting the work conductors between a pair of nodes on the ring. The remaining optical signal power in the optical channel λ _1, for example, propagates in the ring after it has been tapped in a respective node (eg at node C in the clockwise working conductor 810 and at node B at the counter-clockwise work ladder 811 ), is simply terminated at each end of the ladder, as shown. This embodiment is illustrative only. For those skilled in the art, therefore, other means of terminating or otherwise terminating optical channels of a particular wavelength at the ends of the work ladder are readily apparent. It should also be noted that no wavelength conversion is required, and that only one wavelength is required for a full-duplex connection between every two nodes on the 4F-BLSR 800 is needed.

15A and 15B show the operation of the 4F-BLSR 800 in case of a mistake 825 between nodes B and C, where 15A shows communication from node B to node C, and 15B shows a communication from node C to node B. In general, as described above for the above examples, loopback switching is performed with some differences listed below. In this particular example, both nodes implement B and C in response to errors 825 a loopback exchange.

In 15A Node B, which is in loopback mode, forwards the WDM optical signal (including optical channel λ ₁ ) from the clockwise work conductor 810 on the clock counter-sense protective conductor 821 , The WDM optical signal (including the optical channel λ ₁ ) moves through the ring as shown. At node C, the WDM optical signal is looped back from the clockwise anti-sense ground wire 821 back to the clockwise work ladder 810 carried out. Using the broadband coupler based arrangement (not shown) in accordance with the principles of the invention, traffic is then extracted from the optical channel λ ₁ at node C. The remaining optical signal power in the optical channel λ _{1 of} the WDM optical signal clockwise working conductor 810 is then terminated in the manner previously described.

Likewise conducts in 15B Node C, which is in the loopback mode, receives the WDM optical signal (including the optical channel λ ₁ ) from the counterclockwise working conductor 811 clockwise protective conductor 820 , At node B, a loopback switch for the WDM optical signal is sent from the clockwise protective conductor 820 back to the clock counter-direction work ladder 811 carried out. The remaining optical signal power in the optical channel λ _{1 of} the optical WDM signal in the clockwise opposite working conductor 811 is then terminated in the manner previously described. Instead of loopback switching, a well-known SPAN switch can also be used in the 4F-BLSR.

16 shows an illustrative embodiment of a broadband coupler based add / drop arrangement 900 that at the knot 801 to 804 in the 4F-BLSR 800 out 14 and 15 can be used. The structure and operation of the add / drop arrangement 900 in 16 are similar to before for 10 and 13 to some differences with respect to the loopback function described above. For example, the add / drop arrangement for enabling loopback switching between the clockwise work conductor 810 and the clock counter-sense protective conductor 821 a couple of switches 910 and 911 , a broadband coupler 901 , and an associated transmitter 902 , Filters 903 and receiver 904 on. In addition, the add / drop arrangement for enabling loopback switching between the counterclockwise working conductor 811 and the clockwise protective conductor 820 a couple of switches 920 and 921 , one. broadband coupler 915 , and an associated transmitter 916 , Filters 917 and receiver 918 on.

As in the previous embodiments, the switches operate 910 and 911 such as 920 and 921 in a crossbar state, when the Ring is in normal operation (eg without error). Likewise, the switches change 910 and 911 such as 920 and 921 its state to perform the loopback functions, eg, rail state and crossbar state, depending on the position of the error relative to the node. So follow with the add / drop arrangement 900 the operation and flow of traffic in the various directions follow the same principles as described in the previous embodiments.

The The above information is for illustrative purposes only Basic idea of the invention. Professionals are able to numerous orders, although not here expressly be shown or described, yet embody the principles that within the scope of the invention. For example, can the add / drop arrangement according to the principles of the invention are applied to other optical ring architectures than those shown and described in detail herein (e.g. different ring topologies, a different number of Nodes, etc.). The basic ideas of the invention are also equally on optically amplified Networks and networks that do not have optical amplifiers. In addition, professionals will use different combinations of optical and recognize electronic components that are described by the here example structures can be replaced to add / drop and Perform protection switching functions. Accordingly, the Scope of the invention limited only by the following claims.

Claims (10)

Add / drop arrangement that is capable of doing so, at least an optical channel of a wavelength division multiplexed (WDM) signal to add / to a WDM ring network which has a plurality of nodes which are connected via an optical waveguide device are, marked by: at least one of the several Node an optical broadband coupler with a first input, which is coupled to the optical waveguide device to the WDM signal to recieve, a first output for forwarding the diverted first part of the optical signal power of the WDM signal, and one second output for forwarding a second part of the optical Signal power of the WDM signal to the WDM ring network, a receiver that coupled to the first output, the receiver at least Extract an optical channel from the branched first part can, and a transmitter connected to a second input of the optical Broadband Coupler is coupled, the transmitter has an optical Can provide channel added to the WDM signal; and in at least one other of the nodes, means for Preventing the recirculation of an optical channel to interference between optical channels to prevent transporting in the WDM ring network become. The add / drop assembly of claim 1, wherein the means For preventing the recirculation has a wavelength suppression element. The add / drop assembly of claim 2, wherein the means for preventing the recirculation has a wavelength conversion element. An add / drop device according to claim 2, wherein the wavelength suppression element operational is a selected one terminate the optical channel if the selected optical channel is already has passed a node in the network where the selected optical Channel was extracted. An add / drop device according to claim 3, wherein the wavelength conversion element is operational, around a selected one to convert an optical channel of a first wavelength to a second wavelength, if the selected one optical channel of the first wavelength the node with the wavelength conversion element happens before it passes a node in the network where the selected optical Channel should be extracted. An add / drop arrangement according to claim 3, wherein the node, the wavelength suppression element and having the wavelength conversion element, is a central node, the central node further comprising: at least an optical demultiplexer having an input connected to the optical waveguide device coupled, and multiple outputs, wherein the at least one optical demultiplexer separates the WDM signal into individual ones optical channels separates; and at least one optical multiplexer having a plurality of inputs, wherein the at least one optical multiplexer the individual optical channels combined into a composite WDM signal, and the composite WDM signal to the optical waveguide provides, in which the wavelength conversion element between selected outputs the at least one optical demultiplexer and selected inputs of the at least one optical multiplexer is coupled, and wherein the wavelength suppression element to selected outputs the at least one optical demultiplexer is coupled. The add / drop device of claim 1, wherein the WDM ring network is configured in a network topology selected from the group consisting of ei It consists of a unidirectional path-switched ring, a unidirectional line-switched ring, a bidirectional 2-wire line-switched ring, and a bidirectional 4-wire line-switched ring. In a wavelength division multiplexed (WDM) ring network with multiple nodes, over one Optical fiber device are coupled, method for adding / removing at least one optical channel of a WDM signal, wherein optical channel carrying traffic, is transported from a first node to a second node, the method being characterized by: at the second Node branch off a first part of the optical signal power the WDM signal using a broadband optical coupler, Extract of the optical channel carrying traffic, from the first part of the WDM signal, and provide an optical channel, which are added to the WDM signal should, over the broadband optical coupler; Forwarding a second Part of the optical signal power of the WDM signal to the WDM ring network; and at a central node, preventing recirculation of the optical Canal carrying traffic, in the WDM ring network, reducing the interference between optical channels in which WDM signal is reduced. The method of claim 8, wherein preventing the Recirculation has: Suppressing part of the power of the optical signal in the optical channel located at the second node was extracted. The method of claim 8, wherein preventing the recirculation has: Convert a selected optical Channel of a first wavelength to a second wavelength, if the selected one optical channel of the first wavelength passes the central node, before he passes the second node.